The Pasmore Pavillion in Peterlee is a great example of a wonderful structure that was totally wasted on the locals.
http://www.riskybuildings.org.uk/docs/23pasmore/
It’s always being threatened with demolition, but is worth a look even though they’ve removed the stairs and let it get dirty and overgrown now.
Edit: Also, the Dunston Rocket at Gateshead is worth a look, but the area is rough as fuck and I wouldn’t go there alone.